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If you could take a simple, reliable blood test that could spot genetic signs of cancer risk long before the disease ever developed, would you do it?

Some people already have. Breakthroughs in genetics, highlighted by the new human genome “map,” mean scientists can use DNA tests to find genes responsible for certain cancers. Some gene tests already exist for people with family histories of breast and colorectal cancers. Tests for many other cancers may be just a few years away.

Tiny troublemakers

To understand gene testing, visualize the trillions of cells in your body. Inside each cell are 23 pairs of chromosomes made up of long strands of DNA. DNA consists of about 30,000 chemically-coded genes that tell cells exactly what to do: build tissue, fight a germ or even pass instructions on to other cells.

Cells have other amazing abilities. They can copy themselves, turn their genes on and off, “talk” to one another, repair damage to themselves and correct DNA mistakes. But sometimes cells don’t catch their mistakes in time, and these damaged, or mutant, cells begin to make their own flawed copies. These become the breeding ground of cancer, a disease that neutralizes guardian genes while allowing runaway production of the flawed copies.

Inherited cancer cells

We inherit our genetic makeup from our parents, which explains why we resemble them. Unfortunately, we can sometimes inherit a flawed gene, too. Some flawed genes remain harmless throughout life, but others may give rise to malignant tumors. Doctors believe it takes several steps for a cell to turn cancerous—and sometimes all the changes necessary to turn an inherited cell cancerous do not occur.

Studies have shown women who inherit flawed BRCA1 or BRCA2 genes, for instance, have roughly a 50 percent to 85 percent chance of developing breast cancer in their lifetimes. In colorectal cancer, inherited genes account for about 15 percent to 30 percent of all cases. People who inherit such genes have an 80 percent or higher chance of developing colorectal cancer.

Still, most cases of breast and colorectal cancers—and most other types of cancer—develop from nonhereditary causes such as diet, cigarettes or too much sun rather than from the family tree. Consider that only 10 percent of breast-cancer cases result from flawed inherited genes.

Should you be tested?

Gene testing is an extremely personal decision between you and your doctor. On one hand, a positive test result can remove doubts and bring about beneficial lifestyle changes and medical care. But there are negatives, too. The tests aren’t 100 percent accurate, so a genetic flaw could be missed. A patient who learns he or she has inherited a mutant gene can become depressed. A couple’s desire for children, even the marriage itself, may be affected.

Some important questions to ask yourself about gene testing are:

Are you completely sure you want to know the outcome of the test, no matter what the results show?

Is the decision being left entirely up to you and your doctor, or are you feeling pressured by relatives, your spouse or your healthcare provider?

If you test positive for a flawed gene, are there effective ways to prevent or detect the cancer if it, in fact, develops? In extreme high-risk scenarios, for example, some women opt to have their breasts surgically removed rather than face cancer.

Whatever your decision and the outcome, knowing that you carry a high-risk gene is only a warning. Cancer may develop no matter how hard a person tries to avoid it.

Wide-scale testing is still several years away. Difficult issues of ethics, insurance costs and privacy are being addressed by politicians, scientists and health officials. But doctors agree that cutting down on dietary fat, quitting smoking, losing weight, exercising and having regular medical screenings can tip the cancer odds in your favor whether you’ve inherited a genetic problem or not.